1. ‘C’ Programming Structures and Commands
By Aradhya Malhotra

2. Background
C is a general purpose programming language that was founded in 1972 by Dennis Ritchie
Unlike previously developed languages C provides facilities for structured programming and allows lexical variable scope and recursion
It is the predecessor to C++ but and does not support the Object Oriented Programming Style (OOPS) paradigm

3. Structure of C C programs basically contains the following:
Preprocessor Commands
Variables
Constants
Input/output
Functions

4. Preprocessor commands
The #include pre-processor directive is used to link required library files to the main program file (.cpp)
Some of the common header files and their functions are as follows:
Stdio.h : Standard input /output functions
Math.h: Basic math functions such as tan, log, pow(x,y) etc.
String.h: String operations such as strcpy, strcat etc.
Stlib.h: Standard functions such as malloc, rand, srand etc.
Ctype.h: Character classification functions such as isalnum, isalpha, isdigit etc.
Iso646.h: To use macros for logical operators
E.g.
#include<stdio.h>
void main() {
int x;
scanf(“%d”,x); //needs the stdio.h header file }

5. Variables – Data types
In C, variables can be broadly of the following data types:
char – character type
char stringname [x] (x=1,2..n)- string of ‘x’ characters
int array [x] – array containing ‘x’ elements
int- integer type
float- real numbers including decimals etc.
double- extended form of float (larger range)
The above can also be used in conjunction with the following ‘datatype’ modifiers:
long
short
signed
unsigned
cont…

6. Variables – Data types cont...
In addition to the previously described standard datatypes, C allows the following user defined datatypes:
typedef- Allows users to change the name of a standard data type. For e.g. typedef float money will allow the user to use money as a data type
enum- Enumerated data types similar to C++ e.g. enum color{red,blue,white}
struct-
Structures are heterogeneous user-defined datatypes
They are often used to create nodes and lists
They are like the data members of classes but do not have the concept of associated functions
` e.g. struct features{
int height;
double weight;
char[5] color; }

7. Constants In C, constants can be defined in the following two ways-
Using #define
e.g. #define pi 3.14
Using const
e.g. const double x=3.0
Constants are often declared globally instead of being used directly in the main program

8. Input / Output User input from the keyboard is done using ‘scanf ‘
Output to the screen is done using ‘printf’
Here are the format specifiers that are required
%d - int
%c - char
%f - float
%lf -double
%s -string
%x- hexadecimal
For e.g.
#include<stdio.h>
void main() {
int x;
scanf(“Enter integer: %d”,x);
printf(“The integer you entered is: %d,x,”. Goodbye!”); }

9. Functions
Functions are modules or subprograms that accept certain parameters and return values to the calling function / main program
They have the following format:
Return_type function_name(parameters) {
local variables;
C statements;
return return_value; }

10. Additional Concepts Operators and Expressions Arrays Linked Lists
Pointers
Stacks and Queues
Hash Tables